There are approximately 20,000 genes in the human genome. 20,000 packets that house the blueprints for every human cell. And every human cell contains a complete copy of that genome. It’s an incredible feat of bio-engineering. But here’s the question. If every human cell contains every single human gene, how does the cell know what to do? What process determines whether it becomes a pancreas or a patella? And what happens if that process falters—if the right gene is selected but cast in the wrong role.